A front bumper beam is most often fitted in crash boxes, whereas a rear bumper is often fitted directly in the vehicle without crash boxes. In such cases, the bumper beam often has a generally U shape with the central flange pointing outwards from the vehicle and a longitudinal concavity in the central flange. Its fastening portions are provided with high webs so that they perform a function corresponding to the crash box function. The bumper beam may have side flanges with screwholes for fastening to the vehicle as described in SE-527530-C2 or have screwholes in the sides as described in WO-2006/002531-A1.
According to the invention, the concavity deepens progressively towards the end portions of the beam until it constitutes or changes to fastening plates. This makes it possible to fasten the bumper beam to a fastening surface of the vehicle which is narrower than the width of the bumper beam. A further result is a lower profile height of the outer portions of the bumper beam, which may be an advantage from the design point of view. The regions adjacent to the fastening plates are strengthened, resulting in advantageous deformation behaviour in the event of a collision.